Bipolar 96 Cherokee
 

I have a 96 Cherokee that I bought about a year ago. I replaced many parts to get it running good. A few weeks ago it shut off on my wife while driving. Cranked up and got home. Since, some days it starts great and runs, then out of nowhere it dies and is very hard to start. Once started it runs and drives great. Then dies whenever. Now it's hard to start every time, taking 30 seconds or more, to get started. Runs fine, but if you turn it off it's hard to start again. Fuel pressure at rail is 48psig. Injectors work while it's running of course. I am lost. We're going to give it to my son for graduation if I can get it back in dependable shape.

The most likely candidate for the type of symptoms you have described is a failing Crankshaft Position Sensor. It is not the only thing that can cause those symptoms, so if you replace it (Mopar brand recommended) without diagnostics, you may find that the problem persists. The 2nd most likely candidate is an ignition coil that is starting to fail. And the 3rd most likely candidate would be a failing camshaft pickup coil (camshaft position sensor), which is located just under the distributor cap/rotor.

These components can be difficult to troubleshoot when the problem is intermittent, which is why they are often replaced blindly without proper diagnostics by DIY owners. If you like to diagnose the problems properly, your best bet is to catch it in the act on a crank-no-start (be ready to test when that situation occurs). One approach would be to be ready to test the ASD relay and ASD relay fuse to see if it being shut down (stops spark/ignition), if this is observed, it normally rules out the ignition coil (which is downstream). It also helps to strongly implicate the crankshaft position sensor or camshaft sensor. If those 2 components turn out to be good, then the PCM (computer) is implicated, though it is pretty rare for that to be the problem on a 96 (not impossible though).

In this case, I would change the crankshaft position sensor or at least have it in the vehicle to be prepared to change it when it dies while driving. It is a frequent culprit, especially when it dies during driving.

Firing the parts cannon is never the right answer.

CPSs are easy to test, without even removing them. All you need is a voltmeter and some jumpers.

https://www.youtube.com/results?sear...t+a+cps+sensor

Try this
 

My 91xj did the same darn thing and it made me crazy. I call it Syco Jeep. Anyway, mine turned out to be the Auto Shutdown Rekay (ASD) I just took a wire and jumped across the pins that need to be connected and the Syco Jeep runs great. I drove it like that a few months until I got a new relay. Hope this helps.

Take this a gospel. I have part swapped as guesswork too many times, and wasted too much money. Take the extra time to diagnose and save your money

Some basic electrical connectivity and continuity tests can be preformed on a CPS using a multimeter. But it can not be fully tested with a multimeter. These tests can help to show that the CPS -is- the problem if it is having basic electrical connection problems. However, these tests can not definitively show that a CPS -is not- the problem when you are struggling to figure out a no spark, or engine stalling, or other driveability issue.

To see the signal it produces, and to compare that signal in relation to the camshaft position sensor's signal requires an oscilloscope. Even with a scope, sometimes it can't be fully diagnosed because the problems may be happening intermittently or in such away where the signal problems just can't be isolated (or captured on screen). Or the signal looks decent to the human eye, but the computer doesn't like it (for whatever reason), and has trouble reading it.

For the DIY jeep owner, I think having a known-good CPS on hand is probably the most cost/time effective diagnostic. Always keeping one as a good spare.

This is probably best achieved by taking a vehicle before it has any CPS problems, and replacing the sensor with a new Mopar sensor when able. If no problems arise with the new one, then you know you have a good one on the vehicle, and a good one as a spare.

True, but if it is not merely dead, but really most sincerely dead, you can find out with a voltmeter. Another test you can perform with the CPS pulled, is to measure continuity between the supply and signal terminals while holding a hammer or wrench up to the face of the sensor. If it's working, you'll see the change when the steel gets close, and when you pull it away. if you see nothing, it's dead, Jim.

I just did this with my 'new' 2002 WJ. Deader'n a door nail. Popped in a new one, and good to go.


At almost $200 a pop from the dealer, I'm not sure that' a viable plan for most of us.

Oh Man I feel for you I just went through something like this .. it does sound like a crank sensor and hopefully only that in my case I had to replace the PCM among other things But if you have to get a PCM being a 96 it must be numbers matching